We dietitians hear this question a lot: "What's the healthiest type of nut?" Well, just like with other food groups, there is no single nut that reigns supreme. Each type has a unique array of nutrients and phytochemicals. Here, EN summarizes what you can gain when you reach for nuts.

In general, when part of an overall healthy diet, eating nuts is linked to lower rates of Type 2
diabetes
, healthier cholesterol and triglyceride levels, a smaller waist circumference, better blood pressure levels, less insulin resistance, and more. Read on to learn more about five of the most common types of nuts.

1. Almonds. Score one for the heart. Not only does eating almonds in place of less nutritious foods lower LDL ("bad") cholesterol, but it also appears to improve the quality of HDL ("good") cholesterol when following a traditional cholesterol-lowering diet. In a small study, researchers at Pennsylvania State University found that replacing a banana muffin daily with 1 1/2 ounces of almonds led to a greater amount of the largest HDL particles. HDL particles work by ferrying cholesterol from the blood vessels out of the body. Larger HDL-cholesterol particles mean more of the bad stuff can be carried away.

2. Peanuts. As part of the legume family, the peanut is not a true nut. Yet we often group it as a nut because its nutrient profile is more similar to a tree nut than to other legumes, like chickpeas and lentils. Affordability is one of the peanut's major strong suits, however lower price doesn't mean fewer health benefits. Research in JAMA Internal Medicine shows that, just like other nuts, eating peanuts is associated with lower rates of mortality. Americans who consumed peanuts regularly over a five-year period were less likely to die of any cause compared to people who rarely ate peanuts.

3. Pecans. The only major tree nut that is indigenous to America is the pecan. This powerful nut is packed with flavonoids, a family of phytonutrients also found in fruits, vegetables and freshly brewed tea. In a small study of adults with excess abdominal fat, eating about 1/4 cup of pecans daily for four weeks improved insulin sensitivity and other markers of Type 2 diabetes and heart disease. The mechanism of action isn't clear, but the benefit may come from pecans' phytonutrients or from replacing foods with less healthful saturated fats with pecans' healthful unsaturated fats, explains Diane L. McKay, Ph.D., nutrition scientist at Tufts University and a researcher involved in this study.

4. Pistachios. Calorie-counters rejoice because each pistachio weighs in at only 3 calories. Plus, when you eat shell-in pistachios, cracking the shell slows down the snacking process, and the shells serve as a visual reminder of how much you have eaten which may assist with portion control. The green nut is bursting with lutein and zeaxanthin, two relatives of beta-carotene. These two phytonutrients make their way to both the brain and the macula of the eye, where they appear to protect against cognitive decline and age-related macular degeneration.

5. Walnuts. According to a study of about 34,000 American adults, walnuts might cut the risk of developing Type 2 diabetes by half compared to those who don't eat nuts. "For each handful -- increase in walnut intake, the prevalence of diabetes dropped 47 percent. The effect appears to be more potent among women than men," says Lenore Arab, professor emerita of medicine at the David Geffen School of Medicine at UCLA and the primary investigator of this study.

Other research suggests that walnuts are good for the gut. "Walnuts contain a complex array of healthy constituents," explains Daniel W. Rosenberg, Ph.D., HealthNet Inc., chair in Cancer Biology and professor of medicine at the University of Connecticut School of Medicine. They serve up fiber, vitamin E, omega-3 fatty acids, and health-shielding phytonutrients such as ellagitannins, melatonin and polyphenols, he adds.

Rosenberg's research in an animal model suggests that walnuts may protect the colon against cancer-causing compounds while acting as a prebiotic and inducing beneficial changes in the gut microbiome. And in human studies, researchers find that eating about 1/3 cup of walnuts daily may change the gut microbiome in ways that improve digestive health, tamp down inflammation and reduce the risk of
colon cancer
.

(Environmental Nutrition is the award-winning independent newsletter written by nutrition experts dedicated to providing readers up-to-date, accurate information about health and nutrition in clear, concise English. For more information, visit www.environmentalnutrition.com.)